Serum concentrations of Lamictal are not influenced by interactions with non-AEDs, but are markedly increased by an interaction with valproate, which inhibits glucuronidation, the main metabolic pathway of Lamictal. Consequently, the half-life of Lamictal varies according to concomitant therapy. If the patient is taking hepatic enzyme–inducing AEDs, the half-life is 14 hours, whereas if the patient is taking valproate (e.g., Depakote), the half-life is approximately 70 hours. As a result, if valproate is added to Lamictal, the Lamictal dose will probably need to be reduced.

Another consequence of this interaction is that if hepatic enzyme–inducing drugs are withdrawn, the serum concentration of Lamictal will rise. Withdrawing valproate, on the other hand, will lower the Lamictal concentration. Similarly, if oral contraceptives are stopped for 7 days each month, Lamictal levels will increase during that week. Lamictal levels will fall when the oral contraceptive is restarted.

Lamotrigine does not alter the hepatic metabolism of other drugs, including other AEDs.

AED Interaction Sheets:
Seizure drugs are often affected by drug-drug interactions. Print these informative sheets for practical help.

• Interaction sheet for lamotrigine (Lamictal)